The present invention relates to a device and a method for operating an electric machine. The present invention particularly relates to a device and a method for operating an electric machine during a transition of the electric machine to an active short-circuit mode.
Electric machines, such as, for example, permanently excited synchronous machines, are used for numerous technical applications. Electric machines can, for example, be used as a drive for an entirely or partially electrically operated motor vehicle. For safety reasons, provisions must thereby be made for dealing with a possible fault. Such a fault can, for example, be a disturbance or breakdown of a sensor which delivers measured values for a reliable operation of the electric machine. A further fault can, for example, be the breakdown of a supply voltage in an electrically operated motor vehicle. An option for an operating mode in the event of a fault is a free-wheel mode of the electric machine. In so doing, an electric voltage is no longer applied to the electric machine from the outside. The electrical phase connections of the machine are isolated from one another in the process. A further safe operating mode is the so-called active short-circuit. In the case of this active short-circuit, all phase connections of the machine are electrically connected to one another by means of suitable switching elements.
The German patent specification DE 10 2012 101 508 A1 discloses a method and a device which initially operate an electric machine in such an active short-circuit when a loss of a supply voltage occurs. In this case, current rectifier valves in the intermediate circuit of an actuating circuit for the electric machine are closed, and therefore the connections of the electric machine are short-circuited.
A need exists for a device and a method for operating an electric machine, which allow an active short-circuit operation to be introduced in the electric machine in a safe and component-protecting manner.